Apparatus for measuring vapor content of gas



1952 A. A. OBERMAIER APPARATUS FOR MEASURING VAPOR CONTENT OF GAS 4Sheets-Sheet 1 Filed Feb. 23; 1946 hvnrlllviidldlllll Invent 0n wreall062 -272 aer'.

A. A. OBERMAIER APPARATUS FOR MEASURING VAPOR CONTENT OF GAS iled Feb.25, 1945 Dec. 9, 1952 4 Sheets-Sheet 2 Dec. 9, 1952 A. A. OBERMAIER2,621,297

APPARATUS FOR MEASURING VAPOR CONTENT OF GAS Filed Feb. 23, 1946 4Sheets-Sheet 3 I It r g Patented Dec. 9, 1952 APPARATUS FOR MEASURINGVAPOR CONTENT OF GAS Alfred A. Obermaier, Chicago, 111., assignor toIllinois Testing Laboratories, Inc., Chicago, 111., I a corporation ofIllinois Application February 23, 1946, Serial No. 649,567 e 1 My.invention relates, generally, to method of and means for measuring andcontrolling the humidity of gases and it has particular relation totheuse of radiant or infra-red heat for these purposes.

It has long been known that the transmission of radiant heat throughgases varies depending- ,upon the compositionof the gas. That is, theabsorption of radiant heat by gaseous matter depends upon the character.thereof. f

The present invention relates particularly to the measurement ofthediathermancy of' air with a view to determining the water vaporcontent or the dew point thereof. It is desirable to have an accuratemeasurement of the dew point of the air for laboratory test purposes andother purposes so that proper account can be taken of this factor ininterpreting the results. It is also desirable, particularly inconnection with air conditioning systems, to provide'mean's forautomatically controlling the humidity of the air.

It is known that the percent of transmission of infra-red .radiationthrough water varies with the wave length of the radiation Thepercentage of transmission is at a -minimum at a .;wave length of about3 microns and also at a .wave length of about dmicrons. Stated con-,versely, the. infra-red absorption for-water"is a maximum at wavelengths of about 3 and '6 microns. In accordance with the presentinvention advantages taken of this characteristic of water in theapplication there to of a limited band of wave lengths of infra-redradiation for measuring the vapor content of a gas.

. Accordingly, the object of my invention'generally stated, is toprovide a method'of and means ion-employing infra-red heat fordetermining the vapor content of a gas, such as air, which shallbesimple and efficient and which may be readily and economically. used.

Another object is to employ radiant or infra- .red. heat in measuringthe diathermancy of water vapor. I Y 1 A further object :is tomeasure-the diather- :mancy of water vapor over wide ranges oftemperature andpressure. I a Stillv another object is to compare-- the"diathermancy of a test gas with thatof a standard gas in ordertedetermine the diather'mancy-of the former. 3 1: :A still furtherobject is to employ a single source of infra-red heat for making the"com- :parison.

4 Claims. (01. 250-435) ".'Another object is to empIdyYra'diant mar na-'55 '2 ing a narrow range .of wave lengths inorder to increase theaccuracy of the measurements or the control. H A further object. is tocontrol the humidity of gas, such as air, in accordance with itsdiathermancy.

. .Other objects of my invention will, in part, beobvious and in partappear hereinafter,

.For a more complete understanding. ofthe nature and scope of myinvention, reference may be had to the following detailed description,:taken in connection with the accompanying drawings, in which: 1 Figure1 is a sectional view, partlydiagrammatic, which illustrates oneembodimentofmy invention; n .1

Figure 2 illustrates, diagrammatically, a preferred circuit: arrangementfor the temperature sensitive element employed in Figurel so as toaccommodate wide ranges of'temperatures and :pressures; i. I v.; x 1!.2.

Figure 31 isa view, partly inelevationland .partly in section, showinghow the elements making' up the thermopile usedas the temperaturesensitive element in Figure '1, may be arranged; I Figure 4-illustrates, -diagrammatically,- how a resistance element-,-- usedforthe temperature sensitive element in Figure 1, maybe connected .in aWheatstone bridge circuit'to-permit a wide range of measurement; rFigure 5- is a View, in front elevation, of ares'istance element and itsmounting which may be used as the temperature sensitive element inFigure 1; Figure 6 is'a'view, in end elevation, oi the device shown inFigure 5,- a part being broken away to showthe character of the frame;Figure- 7 illustrates; diagrammatically howtwo of the measuring devicesshown in Figural-may 'be employed for comparing the diathermancy of atest gas with that ofa" standard gas; K Figure 8 illustratesdiagrammatically, how-a single source of radiant energy can be employed-fo'r 'makingthe comparison between the gases in "lieu of the separatesources shown in'FigureV Figure 9 illustrates, diagrammatically, how the:present invention can be employed for controlling the humidity of-air;and a Figure 10 shows an alternate form for applying the infra-redradiation to the humidified air-for -mea'suring the humidity thereof forthis purpose -a1'c'ne or rot controlling thehumidity by' -means such asthose illustrated in Figure 9.

, aeiernp -pe'irticularly to' Figure 1 or the drawings; it "will be=ob'serv'ed that the reference 5 pointer 45. is adjusted alongtheresistor 46, so as to bring the needle of the instrument 41 to thede-. sired position along the scale. Preferably the dewpoint of theknown gas is fairly close to that of the unknown gas so that theposition of the pointer 45 along the resistor 46 can be chosen to givethe maximum sensitivity to the instrument .41. V Now the source of. testgas is connected. to the radiation tube It! by opening the valve l3. Thevvalve I5 is opened to allow the test gas to fill the radiation tube Iandto clear it of .the gas pre-. viously contained therein. After asuflicient amount of the test gas has flowed'throughthe radiation tubel0 so as to insure that it contains only'the test gas, the valves l3 andI are closed. Of course, the pressure as indicated by the gauge -H isadjusted so as to be the same for both the standard gas and the test gasso that the measurements will be made under identical pressureconditions. It is also assumed that the current as indicated by themeter 28 for heating the filament 24 will be the same for both testruns. The deflection of the pointer of the measuring instrument 41 isthen noted. If it is the same as for the standard gas then it will beapparent that the test gas has the same dewpoint as the standard gas. Ifthe deflection of the pointer of the instrument 41 is less that obtainedwhen measuring the standard gas then the dewpoint of the test gas iscorrespondingly higher than that of the standard gas. Likewise if thedeflection is higher the dewpoint is lower. The difference in thedeflections of the needle of the instrument 41 may be estimated as apercentage difference of dewpoint since the deflection is directlyproportional to the specific humidty of the gas.

Instead of the thermopile type of temperature sensitive element, asshown at 36 and previously described, being used for measuring theenergy that is transmitted through the radiation tube NJ, a device maybe used which depends on the change of electrical resistance withtemperature. Thisis known as a bolometer. One form of this is i1-lustrated in Figures 5 and 6 of the drawings.

The temperature measuring element of the bolometer is indicated,generally, at 5| in Figure 5 and'may comprise a generally rectangularframe 52 having a window 53 therein. It will be understood that theframe 52 may be suitably mounted in the right hand end of the housing33, Figure 1, in lieu ofthe temperature sensitive element 36 there shownof the thermopile type. The frame 52 may be provided with integrallyformed projections 54 over which a wire 55 may be laced, as illustrated,with the ends being connected to terminals 56. The frame 52 may beformed of ""Ba'kelite and the wire 55 may be of .0001 inch diameterplatinum wire.

With a view to using the bolometer over a relatively wide range the wire55, which forms a tempe'rature sensitive resistor, may be connected inone arm of a Wheatstone bridge, shown generally at 51 in Figure 4 of thedrawings. Resistors 58, 5 9 and 68, which are adjustable, make up theother farms of the bridge. It may be energized from a battery 6| througha variable resistor 62. A galvanometer 63 is connected across the bridge51 for measuring the differential voltage in the customary manner. Theresistors 58, 59 and '60 may be-adjusted to provide for operating thebolometer at different ranges with maximum sensitivity as describedhereinbefore'in connection with the use 0f the biasingbattery 44 for thethermopile type 'of temperature sensitive element 36;

In Figure 7 of the drawings there is shown a system for comparing thediathermancy of two gases, one of standard and the other a test gas; inorder to determine the diathermancy of the latter. It will be noted thattwo measuring de-, vices, shown generally at 66 and 61, are providedeach of which corresponds generally to the device shown in Figure 1 ofthe drawings and described hereinbefore.

Each of the devices 66 and 61 comprises a hous-P ing or radiation tube68 having an inlet conduit .69 and an outlet conduit 10. Valves 1| and12 are provided in the conduits 69 and 10 for controlling the flow ofgas therethrough. Gauges 13 are provided for indicating the pressure inthe radiation tubes 68. The radiation tubes 68 are closed at their endsby windows 14 of quartz and a filter glassshield 15 having thecharacteristics of the filter glass I8 shown in Figure 1 is providedbetween the windows 14 and the upper ends-of the radiation tubes 68 andsources 16 of infra-red radiation. The combination of the quartz windows14 and filter glass shields 15 serves to restrict the wave length of theinfra-red radiation which traverses the radiationtubes 68 to the desiredband, as previously described, corresponding to maximum absorptionthereof by water vapor. The sources 18 may be energized from a suitablecurrent source 11, such as a volt 60 cycle source through variableresistors 18. The sources 16 may be of the platinum or tungsten filamenttype or of the silicon carbide rod type aspreviously described toprovide the desired temperature of .1900 F. Ammeters 19 are provided forindividually measuring the current flow to each of the sources 16.

The energy transmitted through each of the radiation tubes 68 ismeasured by a bolometer element 82'lo'cated in a'housing 83. The element82 may be constructed as shown in Figures 5 and 6 of the drawings anddescribed hereinbefore. They are connected in adjacent arms of aWheatstone bridge, shown generally at 84 in which are located variableresistors 85. The other pair of arms of the Wheatstone bridge 84comprise variable resistors 86. A galvanometer 81 is connected acrossthe bridge 84 and it is arranged, to be energized from a battery 88through a variable resistor-89. I V

In operation a perfectly dry gas may be introduced in each of thedevices 66 and 61 by opening the valves 1| and 12.- After sufiicientamounts of the dry gas have flowed through the radiation tubes 68 toinsure that only this gas remains therein, the valves 1| and 12 areclosed. The bridge 84 is then balanced so tha'tthe galvanometer 81occupies the zero or center position by varying the energization of theinfrared sources 16 through the adjustment of the variable resistors 18.3

After thebridge 84 has been balanced in this manner the test gas may beintroduced into'one of the radiation tubes 58, for example the tubeforming a part of the device 61. The valves TI and 12 thereof are openedfor a length of time suflicient to scavenge the radiation tube 38 and toinsure that the test gas only is contained therein. The valves 1| and 12are then closed.

The pressures within the radiation tubes 68 as indicated by the gauges13 should be the same,

for example they may be of atmospheric pressure.

61 have been closed the reading of the galva- ,nometer 81 is noted.Assuming that the test gas After the valves 1| and 12 of the devicecontains some water vapor, the galvanometer 81 will indicate a'chan-gewhich is proportionalito the amount of moisture in thetest gas. It willbe understood that' the scale o'fithe galvanometer 81may be calibratedin moisture. units or provision may be made for bringing the bridge 384again: into ibalancexby varying the resistors .86: in whichthecalibration may 'be eiiected intermsoi resistancevariation.

While the comparison method has ibeen'described using aperfectly dry gasas a standard, it will be-understood that a. gas having .apredeterminedwater vapor content maybei-use'd as a standard. ln'such'case 'an'attempt would be made'tdselect as a standard gas a.gasihavingza water vapor content nearly approximating i that of-thetest gas. 'Thiswould permit a high? degree of-eccu-racy in measuring thewater vapor 'contentof thetestigas'by comparing itwith .the standardgas, as-w'ill be readily understood.

In FigureB of the drawings a comparisonlsystern isshown in which'asingle source, indicated generally'at 92, of infra-red radiation can "beused. .The source may include a filament 93, of platinum ortungstenwithin a quartzenvelopc 94. Also a silicon carbide rod can:beused to provide the desired temperature of 1900 F. :The filament 93is energized from a source '95.-.sll0h as -a--110'volt 60 cycle source,through a-variable resistorflt. The current flow can-be measured byan-am'meter'el. The filamentBS-and its-envelope' 94 are located withinthe tubular housing 98 that is disposed between a pair of comparsionmeasuring devices indicated generally at ItI and I02. As describedhereinbefore-each of these devices may include a radiation tube-H13having an inlet conduit I04 and an outlet conduit I05. Valves I06 and I?control the flow of gas through these conduits. Assliown. the-conduits Imay be joined in a single outlet conduit I08. The ends-of the radiationtubes I03 are closed by quartz-windows II I. Filter glass shields II2having the characteristics of the filter glass I8 of-Figure 1 may beprovided'onkopposite sides of the source of infra-red radiationwithinthe housing 98 in order to'limit the wave length of the infra-redradiation applied to the: gases in the radiation tubes I03.

I The energies transmitted through the radiation tubes I03 may bemeasured by the measuring devices indicated generally at I I3. These aresimilar-tothe measuring device 32 shown in Figure lot the drawings. 1Each comprises a tubular housing -I I4 disposed in alignment with theradiatlon-tubes I93. Shields H5 and H6 are-provided j- 1or directing theinfrared radiation onto 'a :jbolometer element I I1, preferably in theform of Qa resistance element as shown in- Figures 5 and 6 f of thedrawings.

The resistance elements IIT'are connected in.

The operation of the comparison measuring apparatus shown in Figure 8 issimilar tothatof the apparatus shown in Figure 'I-anddescribedhereinbefore. Accordingly,- the description will not'be repeated here.Of course, it will-be under.- stood that, since a single source ofinfra-red 8 radiation is used in the system: shown in :Figure 8, itwilli be unnecessary to perform the balancing' step of the-sourcesdescribed for Figure All that is necessary willbe to .balance thebridgeH9 or toobserve the indication on the galva nometer' I 22 or withrespecttothescale: I Mas-the case-maybe. I In Figure 9 of the drawingsthere is shown-a system in which the vapor content measuring means of-'a gas :canbe employed for. controlling the humidity thereof. Thissystemncan-beaused advantageously for controlling the humidityof air 1supplied in air conditioning. systems Lor for controlling. the humidityfor air for. test: purposes orfthelike.

'As shown in: the drawings there. is provided an infra-red sourc .I.30at one end of a aradiati'on tubez I3I. The energytransmittedthroughzith'e radiation tube I3 I ;may. be measured by; a heatsensitive: element I32. It will; be recognized: that this: combination50f elements is essentially; the same as shown. .inFigure 1 of thedrawings. and described hereinbefore. However, ;it 'will. be :understood.that a bolometer element is used instead of. the thermopile' formeasuring the energytransmitted through the radiation tube. I*3-I. Thegas flowing through the; radiation tube .13I may be conducted thereto bya conduit I 33.-which is connected to an air duct l34-through-;whichhumidified air flows. .In theduct I34 isalhumidifier l35whic'h is'suppliedwith' air-:by aconduit I36 by means of a blower I31. NozzlesI3B,-.Ia re providedv :in. the humidifier I35 which are; sup-'- plied'with: water. through a, conduitnl39ihaving a control'valve [40 therein.The control-gvalye I 40 may be provided with :an armature -I 4 I; and anoperating winding I42 in, cooperative-relation thereto.

"It "willbe understood that a portion :of;- the humidified air flowingthrough the duct- I34 is conveyed'through the conduit I33 to theradiationztube I3I where the: vapor content. thereof ismeasured. It isexhausted therefrom through an outlet conduit 443. V

The heat-sensitiveelement I32 'isconnected into one arm ofaWheatstone-bridge, shown generallyat I45. .The adjacent arm is formedby a variable resistor I 45. The oppositearms may be formed,respectively, by a carbon pile regulator 4'41 and. a variable resistorI48. -A galvanometer type .relay- 1 49 isconnected across thebridge 4.45for. controlling theopening and closing of contacts -I 50 connected inseries circuit relation with the. winding. I'42.and.- asecondarywiriding I.5I of atransformer, shown generally at I52 whichprovides. a source. of .energization for thei windlu'g 42."Thetransiormer :I 52 has aprimary winding I 531that may be connectedforlenergization across a source I52 of alternating current, .such;as110 volt 60 cycle source. 1

The transformer I52 is provided with another secondary winding J55whichservesto energize a bridge type rectifier, shown. generally ,at.1.56, wili'ch' may. be used jforenergizing'. the bridge nwill beunderstoodhthat the. bridge .145. ms ire-adjusted so as to control theopening and closing of the contacts 150. in .such manner ,.as tomaintaina predetermined humidity in theair passing to the .ductjI34bycontrolling the-degree of opening and closing of the control valveI40. "In; Figure 10 of the drawings thereisillustrated a system inwhichit .is unnecessary to employ the radiation tube I3I-,-as.shown inFigure 9. The infra-red .source .130 may be located on 9 one side of theduct I34 and heat sensitive element I32 may be located on the oppositeside. The duct I34 may be provided with quartz windows I 51 and a shieldI58 of filter glass or the like may be provided in conjunction with theinfra-red source I38 for the purpose of limiting the wave length of theradiation transmitted through the duct I34, as will be readilyunderstood.

Since certain further changes can be made in the foregoing constructionsand different embodiments of the invention can be made without departingfrom the spirit and scope thereof, it is intended that all matter shownin the accompanying drawings or described hereinbefore shall beinterpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. Humidity measuring means comprising, in combination, means providinga source of infrared radiation, a first chamber for containing gas thehumidity of which is known, a second chamher for containing gas thehumidity of which is to be measured, opposite walls of each of saidchambers being formed of fused quartz and aligned with said source, theenergies transmitted from said source through the quartz walls of saidchambers and the gases therebetween being functions of the humidities ofsaid gases, and means for comparing said transmitted energies.

2. Humidity measuring means comprising, in combination, means providinga source of infrared radiation, a first chamber for containing gas thehumidity of which is known, a second chamber for containing gas thehumidity of which is to be measured, opposite walls of each of saidchambers being formed of fused quartz and aligned with said source, theenergies transmitted from said source through the quartz walls of saidchambers and the gases therebetween being functions of the humidities ofsaid gases, a resistor individual to each of said chambers and subjectedto the energy transmitted therethrough whereby the resistance thereof isa function of the transmitted energy, and means for connecting saidresistors in a Wheatstone bridge circuit for comparing the resistancesthereof to indicate the relative humidity of the gas in said secondchamber.

3. The invention, as set forth in claim 1, wherein a single source ofinfra-red radiation is common to both chambers.

4. The invention, as set forth in claim 1, wherein the chambers aredisposed in end to end relation, and a single source of infra-redradiation is located therebetween and is common thereto.

ALFRED A. OBERMAIER.

REFERENCES CITED The following references are of record inthe file ofthis patent:

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